A power splitter is a commonly used component in many optical circuits and systems, including many communication systems. In general, a power splitter divides light from one or more input ports into two or more portions and routes these two or more portions of light to two or more output ports. The simplest power splitter is a 1.times.2 power splitter wherein light from one input port is divided and routed to two output ports.
The power splitter is bi-directional in that light can enter or exit any port in the power splitter. The ports of the power splitter can either be an "input" port or an "output" port, depending upon the direction in which the light travels. Consequently, for the purposes of this description, a port will be designated as an input port if light is being received at that port and as an output port if the light is being emitted at that port.
With a 1.times.2 power splitter, the light on the input port is divided into two portions according to any determined fixed ratio. For instance, one common ratio is 50/50 which means that light entering one port will be divided into one portion which is nominally 50% of the entering light and into another portion which is nominally 50% of the entering light. Another common ratio for a power splitter is 67:33 whereby light is divided into two portions which are 67% and 33% of the entering light power, respectively.
A power splitter, however, is not limited to just a 1.times.2 splitter, but may be designed to divide light from its input port into more than two output ports. Along these lines, in some applications, light from one source needs to be equally divided and routed to more than two locations, such as to three locations. A 1.times.3 power splitter would therefore be used to divide the input light into three parts. An example of a ratio for this type of power splitter may be designated 33:33:33. The ratio 33:33:33 indicates that the splitter is designed to split the entering light into three portions of 33%. Also, another common type of optical power splitter is a 1.times.4 power splitter having a ratio of 25:25:25:25 for dividing input light into four equal portions.
A power splitter can have other design variations as well. For instance, some power splitters are four port devices with two ports being placed on either side of the power splitter. When light is received into either one of the ports on one side of the power splitter, the power splitter divides the light into two portions according to a fixed ratio and routes the two portions of light to the two output ports on the other side of the power splitter.
Typically, a power splitter is individually fabricated from single mode optical fibers to have a certain fixed ratio. The fused biconic taper (FBT) is a common technique used to fabricate power splitters. The FBT is fabricated from two fibers which have been joined in such a manner that light is coupled between the two fibers according to the fixed ratio. The fabrication process involves the steps of heating the two fibers, joining the two fibers together, pulling the fibers until the desired amount of coupling is achieved, cooling the fibers, and packaging the fragile device to protect it from the environment. If light is divided into more than two portions, then additional FBT fiber couplers are cascaded to provide the additional division of light.
Because each power splitter is individually fabricated, the ratio can be precisely set for a given application. For instance, a first power splitter may be formed as a 67:33 power splitter, a second power splitter may be formed as a 50:50 power splitter, and a third power splitter may be formed as a 33:33:33 power splitter by fusing three fibers together. Making power splitters with more than two equal power ports on each side, for example a 1.times.3 power splitter, using FBT is very complicated and expensive. Further, for such desired larger splits and for unbalanced power splitting, FBT couplers are cascaded together to form a power splitting circuit. Furthermore, the splitting ratio of FBT power splitters are not uniform across all wavelengths of interest. Nonetheless, the individual fabrication of each discrete FBT power splitter has an advantage of being able to custom design the desired split ratio of each device.
The serial fabrication of individual FBT power splitters, however, causes the cost of the power splitters to be relatively high. This is especially true for compound power splitter optical circuits requiring the division of light into more than two portions, since these circuits would have an even greater cost due to the use of more than one power splitter concatenated end to end, or the use of power splitters which are comprised of more than two fibers, which are necessarily more expensive due to the more extensive fabrication process and the added cost of interconnecting the different power splitters one to the other. A need therefore exists for a power splitter which is relatively inexpensive.